1. Field of the Invention
The present invention relates to a control device of an internal combustion engine.
2. Description of the Related Art
U.S. Pat. No. 4,485,775 discloses an engine having a helically-shaped intake port, which can create a strong swirl motion in the combustion chamber when the engine is operating at a low speed and obtain a high volumetric efficiency when the engine is operating at a high speed. This helically-shaped intake port includes a helical portion, an inlet passage portion tangentially connected to the helical portion, and a bypass passage connecting the inlet passage portion to the helix terminating portion of the helical portion. A swirl control valve is arranged in the bypass passage.
In this engine, when the engine is operating at a low speed, the swirl control valve closes the bypass passage. As a result, the entire volume of air flows into the helical portion from the inlet passage portion of the intake port, and thus a strong swirl motion is created in the combustion chamber. As mentioned above, in this engine, since it is possible to create a strong swirl motion in the combustion chamber by closing the swirl control valve, a stable combustion can be obtained even if an extremely lean air-fuel mixture is used.
However, where such an extremely lean air-fuel mixture is used, for example when a gear changing operation in the engine transmission is carried out, a satisfactory increase in the output torque of the engine cannot be obtained. That is, when the gear changing operation is carried out, first, the accelerator pedal is released, second, the position of the transmission gear is manually changed and, finally, the accelerator pedal is depressed. At this time, where an extremely lean air-fuel mixture is used, a satisfactory increase in the output torque of the engine cannot be obtained. This unsatisfactory increase in the output torque of the engine causes the driver to feel that insufficient power is available for driving the motor vehicle, and thus a problem occurs in that good drivability cannot be obtained.